JPH07216439A - Production of high nitrogen content steel - Google Patents

Abstract

PURPOSE: To provide a process for producing stabilized ultra-low carbon steel having a high nitrogen content for enameling applications.

CONSTITUTION: The preferable process includes two steps. In the first step, gaseous nitrogen is mixed with gaseous oxygen and the mixture is generated in a basic oxygen furnace for blowing to molten metal through an oxygen lance. After blowing of the oxygen, the carbon content of the molten metal is about 0.03% and the nitrogen content thereof is at least about 0.016 to 0.020%. In the second stage, the molten metal is introduced into a vacuum circulating and decarburizing apparatus where the carbon content of the steel is reduced down to an ultra-low level of about 0.005%. The gaseous nitrogen is introduced to the vacuum decarburization vessel like the gas to be blown through an inert gas tuyere, by which the nitrogen content is maintained at a level of at least about 0.01%.

COPYRIGHT: (C)1995,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the production of steels having a high nitrogen content. More specifically, the present invention relates to a process for producing extra low carbon steel for enameling that is stable for good formability and has a high nitrogen content for excellent enameling properties.

[0002]

2. Description of the Related Art For various applications, steel for enameling must be of high quality having sufficient formability and stretchability in order to be formed into, for example, bathtubs, sinks and the like. The steel is stabilized with reactive alloying elements such as titanium, niobium, boron to add the proper forming properties to the steel. Previously, stabilized enameling steels contained as much as 0.02% carbon. This level of reactive alloying elements is necessary to stabilize this carbon level contained in the innermost layer of steel and producing significant amounts of deoxygenated products such as alumina. To use such steels in many applications to produce satisfactory products requires a great deal of manpower and production costs to completely remove this surface. By utilizing a stabilized ultra low carbon (ULC) steel, i.e. a steel having only about 0.005% carbon, the problems associated with surface defects for the stabilized steel are reduced or weakened. it can. Carbon about 0.0
Steels containing only 05% can be stabilized with small amounts of stabilizing elements, which gives the desired formability and stretchability without surface defects. However, while ultra-low carbon chemical compositions provide the required formability and surface properties, ULC steel alone cannot meet the purpose of enamel. Enameled steels generally require the ability to prevent formation called "hydrogen defects."

The presence of moisture during the enameling of steel will necessarily result in a certain amount of hydrogen dissolved in the solid steel. If the steel does not contain one or several components that trap or retain the hydrogen in the steel, the hydrogen will gradually leave the steel and subsequently coat its surface and cause defects in the enamel covering the surface. The most problematic hydrogen defect in enamel is known as "scale". This problem does not appear for days or weeks after the steel has been enameled, so that this defective steel is incorporated into the final product, for example installed in a new home before the defect itself appears. This results in significant financial damage in time, manpower, productivity, steel manufacturing, product manufacturers and customers. Another enameling defect is the appearance of bubbles or fading on the enamel covering the surface.

It has been found that a high nitrogen content is extremely beneficial in order to obtain satisfactory enameling properties in stabilized ultra low carbon steels. While it is generally desirable to retain a low nitrogen content in ULC steels, while a sufficiently high nitrogen content forms reaction products that trap hydrogen such as TiN, ZrN and BN in the steel, It has been clarified that hydrogen defects are reduced or weakened. These reaction products prevent the release of hydrogen, causing defects in the enamel covering the surface.

One method of incorporating nitrogen into steel is to add nitrogen containing alloys such as magnesium nitride and calcium nitride after the oxygen blowing cycle in a basic oxygen furnace (BOF). However, these alloys are so expensive that they add to the cost of processing and steel. Since such alloys also change the carbon / oxygen ratio in the steel, the vacuum circulating decarburization process often depletes the oxygen present to process the steel to very low carbon levels. RH degasser "upleg"
Nitrogen is also added during the vacuum degassing process by using nitrogen instead of argon as a blowing gas from a tuyere called a snorkel. However, the actual yields are variable and may not give sufficient nitrogen content to prevent hydrogen defects. Nitrogen can also be added in the BOF using an inert gas. However,
This result is also variable and insufficient to achieve the target chemical composition. At times, although the combination of these runs gives the product sufficient nitrogen and carbon, the results of this combination are variable and, with sufficient reproducibility, are required as are the separate runs. Insufficient to achieve the desired steel chemical composition. To provide a steel with sufficient hydrogen absorption capacity to avoid scales and other enameling defects in order to fully meet the formability requirements of final enameling consumers, while achieving proper formability and excess hydrogen It is desirable to use a fully stabilized ultra-low carbon content steel having a nitrogen content of greater than 0.01% to form the inclusions needed for fixation. this is,
It has a significantly higher nitrogen content than conventional ultra low carbon steels, typically only about 0.006% or less. This combination of requirements is unique to enameling steel and requires development of the inventive process. The conventional invented method is for producing an ultra low carbon steel for enameling, and it has been impossible to maintain a sufficient level by increasing the nitrogen content.

[0006]

The process of the present invention allows for the production of steel chemistries for optimum enamel, that is, very low carbon steels stabilized with a high nitrogen content. The preferred steel chemical composition has a carbon content of about 0.005 wt% or less and a nitrogen content of about 0.01 wt% or more. First, this optimum steel chemistry can be consistent and economical. By various devices known to the present inventor,
It is possible to make this steel on a conventional basis with reproducible results.

The method of the present invention is intended primarily for application in basic oxygen processes. In a preferred embodiment, the method is used in a basic oxygen furnace (BOF). As is known in the art, oxygen lances in metallurgical vessels, which are typically suitable for blowing high pressure streams of oxygen, are charged with molten iron, steel scrap and other components to form steel products. The entering a basic oxygen step typically comprises. A high velocity stream of high purity oxygen is blown from the lance into the molten iron starting material to refine the iron starting material into steel. The details of the general basic oxygen process, especially the basic oxygen furnace (BOF), are well known to those skilled in the art. Similarly, as is well known to those skilled in the art for producing ultra-low carbon steel, once the carbon content is reduced by the oxygen blowing step, there is a vacuum circulation decarburization method (CVD) called a vacuum degassing apparatus. With the additional decarburization step, the carbon content of the melt is further reduced to a very low level. In the vacuum decarburization step, since the molten metal is introduced into a low pressure atmosphere, a reaction product of carbon and oxygen such as carbon monoxide is released from the molten metal as a gas reaction product. Occasionally, added oxygen is introduced into the bath of molten iron during decarburization to adjust the ratio of carbon and oxygen for optimum carbon release. As known to those skilled in the art, an inert gas is also typically introduced through the tuyere submerged in the bath to lower the CO partial pressure and sway and agitate the bath. The preferred method of the present invention involves a two stage approach in which the molten steel is treated during both the oxygen blowing step and the subsequent decarburization step. Although the method is described herein with respect to a basic oxygen furnace and vacuum degasser, it will be appreciated that other oxygen blowing steps known to those skilled in the art may be applied.

The first aspect of the process of the present invention introduces nitrogen gas into the molten iron charge at some point during the oxygen blowing cycle. Ideally, you would mix nitrogen gas with oxygen,
The mixed gases are blown together through an oxygen lance into the melt. It is possible to inject nitrogen directly into the oxygen reaction zone, which is the region within the melt where oxygen reacts and ignites the molten charge. Since it is the hottest region of the melt, the maximum amount of nitrogen is contained in the solution in this region. Although no theoretical boundary can be established, the temperature in this region is sufficient to form one atom nitrogen from the poorly soluble two atom nitrogen, so the solubility of nitrogen is highest in this oxygen reaction zone. It is believed that. Nitrogen gas usually occurs as diatomic N ₂ molecules with little or no solubility in liquid iron. However, it is believed that the temperature exhibited by the oxygen reaction zone during blowing is sufficient to generate monovalent nitrogen, which is substantially easier to dissolve in liquid iron. Therefore, introducing gas together through an oxygen lance is an optimal means of ensuring maximum nitrogen uptake, but nitrogen injection does not mean that a second lance with sufficient pressure to bring nitrogen into the reaction zone. Can be accomplished by other means, such as In theory, this could also be done through the tuyeres of the furnace. However, the tuyere
The tuyere needs to be modified to blow at sufficient pressure to bring the nitrogen into the melt, as it blows at significantly lower pressure than the lance. Of course, the introduction of nitrogen through a given lance or lances can be increased with nitrogen introduction through tuyeres and / or nitrogen-containing alloy additives.

Since the cooling effect by the introduction of nitrogen gas is weak, the nitrogen gas is preferably introduced into the lance flow after a sufficient time has elapsed for the blowing of oxygen to start the reduction of the carbon content of the molten metal. It is also desirable to raise the target blow temperature above that normally used for a given charge to compensate for any cooling effects. As is known in the art, the oxygen bubbling process is typically completed within about 20-35 minutes. In the first step of the method, about 5
Since it contains a dissolved oxygen content of more than 00 ppm, the carbon content of the molten metal is about 0.02-0.03w based on the weight of steel.
t%. The nitrogen content after the first stage is at least about 0.01-0.015 wt, based on the weight of the steel.
Must be%. Preferably after the first stage the nitrogen content is greater than 0.015 wt%. If the nitrogen content is too low, the melt is blown again with a mixture of oxygen and nitrogen. After the first stage, a very low carbon level gives a good carbon / oxygen ratio for successful vacuum decarburization, about 1
In order to exceed the carbon content of 50 ppm, the oxygen content of the melt needs to be preferably controlled. The melt is then conveyed to a vacuum degasser to obtain a very low carbon level.

In the second stage, the heat is further processed to very low carbon levels by vacuum decarburization. The problem at this stage is that it slows the consumption of nitrogen, provided that sufficient oxygen is present to remove the carbon. Although the theory does not set a boundary, the nitrogen consumption from the decarburizer is
It is possible to operate by at least two mechanisms. First, the vacuum reduces the partial pressure of nitrogen above the bath. This drop changes the equilibrium between dissolved nitrogen in and around the steel, consuming it by simple boiling. The second point of nitrogen consumption is "scribing" due to CO foam produced when the heat is decarburized.
bing) effect. This second effect is addressed by the present invention.

Due to the use of nitrogen gas as the blowing gas through the tuyere of the degasser, some CO foams form a "salt" with the nitrogen and the tendency of these foams to remove or "clean" the nitrogen from the bath. To reduce. Introducing nitrogen gas into the degasser through the tuyere is the preferred method. However, there may be other ways of introducing nitrogen into the melt during the decarburization process as known to those skilled in the art.
The amount of CO evolved during decarburization is then limited by entering the degasser at the starting carbon level already made relatively low in the oxygen blowing step. Of course, if the carbon content of the melt is not yet high enough when introduced into the degasser, to provide sufficient stoichiometry for CO generation or to further reduce the CO partial pressure. Sometimes, to use argon or an inert gas from the tuyere,
It is necessary to introduce oxygen into the bath during vacuum decarburization. In the latter case, argon can be mixed with the nitrogen passing through the tuyere, and the two gases can also be blown through the tuyere in an alternating manner.

In the second stage of the invention, the steel is about 0.
It is processed to very low carbon levels below 005% while possessing a high nitrogen content above about 0.01%. The resulting steel has excellent formability, and the resistance to hydrogen defects formed by this steel makes it particularly suitable for final high enameling applications. According to the above, the present invention provides a method for producing a high nitrogen content steel from a charge containing a large amount of molten iron.
A preferred method comprises blowing oxygen gas into the molten iron charge and blowing the molten iron with a first portion of nitrogen gas to reduce the carbon content of the iron.
At least a portion of the molten charge is then introduced into the low pressure atmosphere to further reduce the carbon content of the iron, while a second portion of nitrogen gas is introduced into the molten iron. Such a method yields an optimum chemical composition for stabilized ultra low carbon steel for enameling. In a preferred embodiment, the first portion of nitrogen gas is introduced into the oxygen reaction zone of the molten iron. This is a mixed gas stream from a high pressure lance that contains a first of oxygen gas and nitrogen gas.
This is preferably achieved by blowing the part. Preferably, the nitrogen gas is about 5 wt% based on the weight of the mixed oxygen and nitrogen gas blown into the molten iron.
An amount of about 20 wt% is blown. In a preferred embodiment, the low pressure atmosphere is a vacuum degasser and the second portion of nitrogen gas is introduced through the tuyere of the vacuum degasser.

In another embodiment, the carbon content of the iron is reduced to no more than about 0.03 wt% based on the weight of the molten iron prior to introducing the molten iron into the low pressure atmosphere.
In this preferred embodiment, sufficient nitrogen gas is introduced into the molten iron to provide a nitrogen content of about 0.01 wt% or greater based on the weight of the molten iron prior to introduction into the low pressure atmosphere. Preferably, the molten iron is maintained in a low pressure atmosphere until the carbon content of the iron is reduced to about 0.005 wt% based on the weight of the molten iron. In yet another preferred embodiment, the charge is 1 selected from the group consisting of titanium, boron and zirconium.
It is prepared by including more than one element.

Many additional features, advantages and more considerations of the present invention result from the means and actions to solve the following problems.

[0015]

The preferred first step of the process is the necessary starting material, typically about 75.
% Molten iron and 25% scrap grade, after charging in a basic oxygen furnace. This ratio is determined by the heat and the volume balance of a given charge. In order to achieve the required chemical composition and supply the necessary nitrogen gas,
The high pressure nitrogen gas line is drawn into the main oxygen line of each oxygen tuyere of the BOF converter. This nitrogen line is drawn into the oxygen line between the lance and the oxygen flow regulator so that the oxygen and nitrogen sources can be regulated independently. In order to compensate for the thermal effects of nitrogen gas, the target temperature for blowing may be raised above the normal target temperature for a given charge. For example, the target temperature can be increased by about 40 ° F (22. ° C), so instead of ensuring a target temperature of 2950 ° F (1621 ° C) for blowing, 2990 ° F (1643 ° C).
A target temperature of (° C.) may be set. Alternatively, the oxygen bubbling sequence begins in the usual manner known to those skilled in the art for BOF processing. The aim at this stage is between about 0.02-0.03%, preferably about 0.028%, in order to give the maximum possible nitrogen uptake during the blowing period when a minimum amount of CO gas is generated. It is to reduce the carbon content.
Target temperature, oxygen capacity and duration of insufflation will vary from charge to charge. Suitable calculations of the blowing coefficient are well known to those skilled in the art.

When the BOF oxygen blowing sequence is fully achieved and the carbon content of the steel is reduced, nitrogen is added to the oxygen line. Ideally, the nitrogen flow begins at the point of insufflation at which approximately 65% of the expected oxygen volume has been insufflated. At this point, the velocity of the oxygen flow is approximately 19,000 standard cubic feet per minute (SCFM) (537.7 m ³ / mi).
n). Nitrogen has about 3,000 SCFM (84.9).
The flow velocity was m ³ / min). Blow at the required oxygen equilibrium to increase the nitrogen content of the bath, so that the resulting mixture of oxygen and nitrogen can be blown into the bath through the oxygen tuyeres while continuously reducing carbon. To The introduction of nitrogen into the oxygen stream does not affect the total amount of oxygen required as it reaches the end point calculated by heat and volume balance.

The nitrogen gas content of the stream from the oxygen tuyere is
About 5 to 20 wt% based on the weight of stream nitrogen and oxygen. Preferably the nitrogen content is about 10%. If the nitrogen content is too low, insufficient nitrogen will dissolve to prevent hydrogen defects in the enamel product. If the nitrogen content is too high, there will not be enough oxygen in the stream to ignite and react the charge, substantially reducing the carbon content. Before proceeding to the second stage of the method of the invention,
At the midpoint, the dissolved nitrogen content is measured. Based on the measured nitrogen content, the final nitrogen content is at least 0.01-0.015% before being advanced to the degasser.
You must take corrective measures to ensure that When the nitrogen content is 0.01% or less, the melt is
Reblowing is accomplished with a stream of mixed nitrogen and oxygen.
When the nitrogen content is between about 0.010 and 0.015%, it is desirable to add magnesium nitride or a similar nitrogen containing alloy during tapping. For a typical charge, about 1500 pounds (680.5 kg) of magnesium nitride is added. If the nitrogen content exceeds about 0.015%, the melt can be treated in an unmodified degasser. However, in some cases it is desirable to combine several nitrogen addition techniques to further increase the nitrogen content even before the end of the initial blowing sequence. For example, a nitrogen-containing alloy such as magnesium nitride can be added to the melt and / or nitrogen gas can be introduced into the melt through the tuyere of the BOF to increase the nitrogen supply.

In addition to the nitrogen content of the heat being about 0.01% or higher, the oxygen content of the bath exceeds 150 ppm or more and exceeds the carbon content before tapping. The application of technology typically allows a thermal chemistry to be obtained. Moreover, prior to tapping, the carbon content can be limited to 300 ppm or less.
This gives an excellent chemical composition for the second decarburization state. The combination of low carbon, high nitrogen and sufficient oxygen and nitrogen moieties is important for ultra low carbon grade steel products for enameling.

At the completion of the first stage of the process of the present invention, the steel exits the BOF at about 0.03% carbon. In the second stage, the carbon content was 0.0025 in the vacuum degasser.
To 0.005% very low carbon range. By carrying out the second stage of the process of the invention, the average carbon content can be kept above about 0.012%. Except that the blowing gas injected into the vacuum circulation process (VCP) vessel through the inert gas tuyere changes according to the nitrogen content of the molten metal charged, to a very low carbon level in the vacuum degasser. The processing proceeds as usual in vacuum circulation decarburization. The carbon content of the molten metal charged is about 0.
If less than 016%, the blown gas through the tuyere comprises all nitrogen gas. When the carbon content of the charged melt is between about 0.016 and 0.020%, the blowing gas comprises a mixture of nitrogen and argon or other inert gas. The carbon content of the molten metal charged is
Above about 0.020%, it is not necessary to introduce any nitrogen into the VCP and the blowing gas comprises all argon or other inert gas. As the decarburization step proceeds, the nitrogen content of the heat is reduced to the desired product range of 0.010 to 0.015%, as shown in the following non-limiting examples.

[0020]

EXAMPLE A basic oxygen furnace with 558,000 pounds (25
3.11 tonnes of molten iron, 68,000 pounds (3
0.84 tonnes of scrap, 14,000 pounds (6.35 tonnes) of calcined lime and 8,000 pounds (3.63 tonnes) of dolomitic lime were charged. Target drop temperature is 2950 ° F (1621 ° C) with 0.030% carbon.
℃). Calculated oxygen capacity is 473,000s
It was cf (13.386 m ³ ).

The blowing order is 23,000 scfm
(550.9m³/ Min) oxygen flow rate, and 19
0 psig (13.4 kg / cm²) Oxygen pressure of 14
It started at 44 minutes. 300,000 scf (8,49
0m³) Amount of oxygen and then oxygen
The dose increase started. 400 psig (28.1 kg / cm
²) Pressure about 2500scfm (70.8m³) Amount
Nitrogen gas was poured into the oxygen line and mixed nitrogen and acid
The total flow rate of the element is 198 psig (13.9 kg / c).
m²) Line pressure of 25,000 scf (707.5
m³) Held in the amount of. 450,000scf in total
(12,735m³) Amount of oxygen is blown and nitrogen is
By the time this gas mixture was bubbled through. Oxygen blow
The imprint is 474,000 scf (13,414 m³)
It ended at 15:06 with the oxygen amount. Actual blowing temperature
The temperature reached 2963 ° F (1628 ° C). Melting during tapping
The chemical composition of hot water is 0.024% carbon, 0.016% nitrogen.
And 537 ppm oxygen. Additives when tapping
Not added.

The molten metal was moved to the heating station of the ladle metallurgical apparatus, and while heat (vacuum amount) was held for vacuum treatment, the molten metal was heated to 6000 KWH.
Electrical energy was added to the heat. During the hold time, 40 lbs (18.1 kg) of antimony was added to give a product containing 0.005-0.010% antimony. 272 lbs (123.4 k) to balance 0.021% carbon and 533 ppm oxygen
A small amount of aluminum additive of g) was added (measured at the heating station). The melt was held in the heating station for about 1 hour.

After leaving the heating station, the heat was transferred to the degasser of the vacuum circulation process (VCP). An oxygen content of 462 ppm was measured upon arrival of the VCP. Degassing is 17
Starting at 056, the decarburization cycle continued until 18:07. The obtained container pressure was 3.4 torr.
Based on the amount of nitrogen charged, all of the argon blown gas was used. Alloy additions during VCP include 600 lbs (272.2 kg) of aluminum and 600 lbs (2
72.2 kg) ferro titanium, 500 lbs (2
26.8 kg) ferroniob, and 300 pounds (1
It was low carbon magnesium (36.1 kg). After degassing, the heat was 2895 ° F (1590 ° C). The chemical composition of the heat is 0.0018% carbon, 0.
011% nitrogen, 0.058% niobium, 0.0
It was 74% titanium, 0.060% aluminum, about 0.007% antimony, and 0.12% magnesium.

Various modifications and variations of the present invention are possible to those skilled in the art in light of the above disclosure. It is therefore understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically shown and described.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Robert Brossey USA, Indiana 46368, Portage, Box 1014, Rhodgen Road 34 (72) Inventor Gregory Wottell USA, Indiana 46410, Merrillville, Peas Place 7437

Claims (21)

[Claims] 1. A method for producing high nitrogen content steel from a charge containing molten iron, comprising: (a) blowing oxygen gas into the molten iron to increase the carbon content of the iron. Reducing, (b) blowing a first portion of nitrogen gas into the molten iron, (c) introducing at least a portion of the molten iron into a low pressure atmosphere to reduce the carbon content of the iron component. Further reducing, and (d) a method for producing a high-nitrogen-containing steel, which comprises the step of introducing a second portion of nitrogen gas into the molten iron while in the atmosphere. 2. The high nitrogen content steel of claim 1, wherein blowing oxygen into the molten iron creates a high temperature oxygen reaction zone and introduces a first portion of the nitrogen gas into the oxygen reaction zone. Method of manufacturing. 3. Directing the gas toward the molten iron by blowing a first portion of the oxygen gas and the nitrogen gas as a mixed gas stream from an adapted high pressure lance. A method for producing the high nitrogen content steel according to claim 1. 4. The gas first portion of the nitrogen is about 5 based on the weight of oxygen gas and nitrogen gas blown into the molten iron.
4. A method of making a high nitrogen content steel according to claim 1 or 3 comprising blowing from about 20 wt%. 5. The method for producing a high nitrogen content steel according to claim 1, wherein the low pressure atmosphere is a vacuum degassing device. 6. The method of producing a high nitrogen content steel of claim 5, comprising introducing the second portion of the nitrogen gas through tuyere of the vacuum degasser. 7. Prior to introducing the molten iron into the low pressure atmosphere, including reducing the carbon content of the iron to about 0.03 wt% or less based on the weight of the molten iron. The method for producing a high nitrogen content steel according to claim 1, which comprises: 8. A nitrogen content of about 0.01 wt% based on the weight of the molten iron is introduced by introducing sufficient nitrogen gas into the molten iron before introducing into the low pressure atmosphere.
%. The method for producing a high nitrogen content steel according to claim 1, further comprising: 9. Maintaining the molten iron in the low pressure atmosphere reduces the carbon content of the iron to about 0.005 wt% based on the weight of the molten iron. A method for producing the high nitrogen content steel according to claim 1. 10. A method for producing a high nitrogen content steel according to claim 1, comprising providing the charge containing one or more elements selected from the group consisting of titanium, boron and zirconium. . 11. A method for producing a high-nitrogen-containing steel from a charge containing molten iron, comprising: (a) blowing oxygen gas into the molten iron to increase the carbon content of the iron. Reducing, (b) blowing a part of nitrogen gas into the molten iron, and (c) introducing at least a part of the molten iron into a low-pressure atmosphere to reduce the carbon content of the iron. A method of producing a high nitrogen content steel comprising the steps of further reducing. 12. The high nitrogen content steel of claim 11, wherein blowing oxygen into the molten iron creates a high temperature oxygen reaction zone and introduces a first portion of the nitrogen gas into the oxygen reaction zone. Method of manufacturing. 13. A first of the oxygen gas and the nitrogen gas, such as a mixed gas stream from an adapted high pressure lance.
The method of producing a high nitrogen content steel of claim 11 comprising directing the gas toward the molten iron by blowing a portion. 14. The first portion of the nitrogen gas is about 5 based on the weight of oxygen gas and nitrogen gas blown into the molten iron.
~ 1 comprising about 20 wt% spraying.
A method for producing the high-nitrogen content steel according to Item 1 or 13. 15. The method for producing a high nitrogen content steel according to claim 11, wherein the low pressure atmosphere is a vacuum degasser. 16. The method comprises reducing the carbon content of the iron to about 0.03 wt% or less based on the weight of the molten iron before introducing the molten iron into the low pressure atmosphere. The method for producing the high nitrogen content steel according to claim 11, comprising: 17. By introducing sufficient nitrogen gas into the molten iron before introducing into the low pressure atmosphere,
The nitrogen content is about 0.02w based on the weight of the molten iron.
The method for producing a high-nitrogen-containing steel according to claim 11, which comprises adding t% or more. 18. Retaining the molten iron in the low pressure atmosphere to reduce the carbon content of the iron to about 0.005 wt% based on the weight of the molten iron. A method for producing the high nitrogen content steel according to claim 1. 19. A method of producing a high nitrogen content steel from a charge containing molten iron, comprising: (a) blowing oxygen gas into the molten iron to increase the carbon content of the iron. Reducing, (b) blowing a first portion of nitrogen gas into the molten iron so that the nitrogen content of the molten iron is at least about 0.020 wt% based on the weight of the molten iron.
Producing a high nitrogen-containing steel, comprising the steps of: (c) further reducing the carbon content of the iron by introducing at least a part of the molten iron into a low-pressure atmosphere. how to. 20. Maintaining the molten iron in the low pressure atmosphere reduces the carbon content of the iron to about 0.005 wt% based on the weight of the molten iron. A method for producing a high nitrogen content steel according to claim 19. 21. A method for producing an ultra low carbon high nitrogen steel for enamel coating, comprising: (a) blowing oxygen into a bath of molten iron,
Reducing the carbon content of the iron (b) introducing nitrogen gas into the molten iron together with the oxygen (c) exposing the bath to a low pressure atmosphere to further increase the carbon content of the iron Reducing, and (d) by introducing additional nitrogen gas into the molten iron while the iron is exposed to the low pressure atmosphere,
A method for producing an ultra low carbon high nitrogen steel for enamel coating, comprising the step of producing an ultra low carbon steel having a high nitrogen content suitable for coating an enamel.